Solid-state NMR data support a helix-loop-helix structural model for the N-terminal half of HIV-1 Rev in fibrillar form

Rev is a 116 residue basic protein encoded by the genome of human immunodeficiency virus type 1 (HIV-1) that binds to multiple sites in the Rev response element (RRE) of viral mRNA transcripts in nuclei of host cells, leading to transport of incompletely spliced and unspliced viral mRNA to the cytoplasm of host cells in the latter phases of the HIV-1 life cycle. Rev is absolutely required for viral replication. Because Rev aggregates and fibrillizes in solution at concentrations required for crystal growth or liquid state NMR measurements, high-resolution structural characterization of full-length Rev has not been possible. Previously, circular dichroism studies have shown that approximately 50 % of the Rev sequence adopts helical secondary structure, predicted to correspond to a helix-loop-helix structural motif in the N-terminal half of the protein. We describe the application of solid-state NMR techniques to Rev fibrils as a means of obtaining site-specific, atomic-level structural constraints without requiring a high degree of solubility or crystallinity. Solid-state NMR measurements, using the double-quantum chemical shift anisotropy and constant-time double-quantum-filtered dipolar recoupling techniques, provide constraints on the phi and psi backbone dihedral angles at sites in which consecutive backbone carbonyl groups are labeled with (13)C. Quantitative analysis of the solid-state NMR data, by comparison with numerical simulations, indicates helical phi and psi angles at residues Leu13 and Val16 in the predicted helix 1 segment, and at residues Arg39, Arg 42, Arg43, and Arg44 in the predicted helix 2 segment. These data represent the first site-specific structural constraints from NMR spectroscopy on full-length Rev, and support the helix-loop-helix structural model for its N-terminal half.

Elongation of the BH8 beta-hairpin peptide: Electrostatic interactions in beta-hairpin formation and stability

An elongated version of the de novo designed beta-hairpin peptide, BH8, has allowed us to gain insight into the role of electrostatic interactions in beta-hairpin stability. A Lys-Glu electrostatic pair has been introduced by adding a residue at the beginning and at the end of the N-terminal and C-terminal strands, respectively, of the beta-hairpin structure, in both orientations. The two resulting peptides and controls having Ala residues at these positions and different combinations of Ala with Lys, or Glu residues, have been analyzed by nuclear magnetic resonance (NMR), under different pH and ionic strength conditions. All of the NMR parameters, in particular the conformational shift analysis of Calpha protons and the coupling constants, (3)J(HNalpha), correlate well and the population estimates are in reasonable agreement among the different methods used. In the most structured peptides, we find an extension of the beta-hairpin structure comprising the two extra residues. Analysis of the pH and salt dependence shows that ionic pairs contribute to beta-hairpin stability. The interaction is electrostatic in nature and can be screened by salt. There is also an important salt-independent contribution of negatively charged groups to the stability of this family of beta-hairpin peptides.

Effect of cryopreservation on human articular chondrocyte viability, proliferation, and collagen expression

Autotransplantation of human chondrocytes is an alternative therapeutic treatment for focal lesions of cartilage. During the process of isolation and culture of chondrocytes some problems that render the implantation of the cells unsuitable can occur. For security, some cells must be stored using cryopreservation. The objective of this study was to analyze the effect of cryopreservation on cellular viability, proliferation, and collagen expression of human chondrocytes. Human osteoarthritic cartilage (n = 23) was obtained and transferred to a sterile flask containing Dulbecco's modified Eagle's medium (DMEM) and antibiotics. Chondrocytes were isolated, cultured for 3-4 weeks, and frozen in DMEM containing 10% human serum and 10% dimethyl sulfoxide by use of three different protocols. A cellular fraction was frozen directly to -80 degrees C (Protocol I). Another fraction was directly frozen to -80 degrees C and 24 h later introduced into liquid nitrogen (Protocol II). The last aliquot was frozen with controlled freezing using a freezing rate of -1 degrees C/min to a temperature of -40 degrees C, 2 degrees C/min to -60 degrees C, and 5 degrees C/min to -150 degrees C (Protocol III). Cells were cryopreserved for 2 weeks. Cells from each cryopreservation method were then cultured for 7 days and cellular proliferation was evaluated by the counting of the total cells in each flask. Cryopreservation had a negative effect on chondrocyte survival and proliferation. The survival after cryopreservation with the three protocols was 70-75%. There was no significative difference between the methods used to cryopreserve (P = 0.4117). However, there was a significant difference among the donors (P = 0.0111). Cellular proliferation of chondrocytes was reduced by cryopreservation (P = 0.024). The rate of proliferation of different groups was control samples 6.56, Protocol I 4.66, Protocol II 4.69, and Protocol III 5.58. Statistical analysis showed that the programmed protocol was the best method to preserve cellular functions. Chondrocytes were able to express collagen type II 1 week after cryopreservation. Cryopreservation modifies the survival and proliferation of chondrocytes. Of all protocols used to cryopreserve, the programmed protocol seems to be the best technique. Cryopreservation does not alter the collagen type II expression.

Removal of bowel aerobic gram-negative bacteria is more effective than immunosuppression with cyclophosphamide and steroids to decrease natural alpha-galactosyl IgG antibodies

Natural alpha-Galactosyl (Gal) antibodies play an important role in the rejection of pig xenografts by humans and Old World monkeys. In this study we investigate the efficacy of two different strategies to reduce the serum level of natural anti-Gal antibodies. On the one hand, removal of aerobic gram-negative bacteria from the intestinal flora, because anti-Gal antibodies appear to be produced as a result of the continuous sensitization by these microorganisms. On the other hand, we studied the effect on these antibodies of an immunosuppressive regimen of cyclophosphamide and steroids. Ten baboons were treated for three months with norfloxacin (Nor Group; n=6) or cyclophosphamide and steroids (CyP Group; n=4). A further four baboons did not receive any treatment (Control Group). Aerobic gram-negative bacteria became negative in stools of the Nor Group after two weeks of treatment, and remained undetectable until week 7. Thereafter, a gradual increase on the fecal concentration of aerobic gram-negative bacteria was observed despite the norfloxacin treatment. The mean anti-Gal IgG in the Nor Group gradually declined from week 4 to 9 to a mean of 62.7 +/- 18% of the baseline level, and during this period were significantly lower than in the CyP (P<0.02) and the Control (P<0.05) groups. No differences were observed between the three groups during the 16 weeks of follow-up in serum levels of anti-Gal IgM, hemolytic anti-pig antibodies, total IgG, IgM and IgA. In conclusion, removal of normal aerobic gram-negative bacteria from the intestinal flora is more effective than immunosuppression with CyP and steroids in reducing the level of natural anti-Gal antibodies, although there is no discernible effect on IgM antibodies.

Effect of antiinflammatory drugs on COX-1 and COX-2 activity in human articular chondrocytes

OBJECTIVE

To study the effect of steroidal and nonsteroidal antiinflammatory drugs (NSAID) on cyclooxygenase (COX-1 and COX-2) activity in human articular chondrocytes.

METHODS

Chondrocytes were isolated from articular cartilage of donors with no articular disease. Unstimulated and interleukin 1 (IL-1) stimulated chondrocytes were used as models to study the effects of drugs on COX-1 and COX-2. Cells were incubated with vehicle or drugs; supernatants were removed and the level of prostaglandin E2 (PGE2) in each sample was determined by enzyme immunoassay. IC50 were calculated from the reduction in PGE2 content by different concentrations of the test substance by linear regression analysis.

RESULTS

COX- mRNA was detected in unstimulated cells, but stimulation with IL-1 for up 12 h did not modify the levels of COX-1 mRNA. In contrast, COX-2 mRNA was not detectable in unstimulated cells, but it was induced by IL-1. Dexamethasone inhibited COX-2 mRNA expression induced by IL-1. COX-2 protein levels correlated with mRNA expression. Dexamethasone was the strongest drug inhibitor of COX-2 (IC50 = 0.0073 microM). However, it did not inhibit COX-1 activity. Among all NSAID tested, meloxicam and aspirin were the least potent inhibitors of COX-1 (IC50 = 36.6 microM and 3.57 microM, respectively). Indomethacin and diclofenac were the most potent inhibitors of COX-1 (IC50 = 0.063 microM and 0.611 microM, respectively) and COX-2 isoforms (IC50 = 0.48 microM and IC50 = 0.63 microM, respectively). Meloxicam was a more potent inhibitor of COX-2 (IC50 = 4.7 microM) than aspirin (IC50 = 29.3 microM) and similar to piroxicam (IC50 = 4.4 microM). Among all drugs tested dexamethasone showed the greatest selectivity for COX-2 and meloxicam was the NSAID with the best COX-2/COX-1 ratio (r = 0.12). Aspirin and piroxicam were about 8 times more active against COX-1 than COX-2, indomethacin was 7 times more active, and diclofenac was an equipotent inhibitor of COX-1 and COX-2.

CONCLUSION

We found that COX-1 and COX-2 isoforms are expressed in human chondrocytes at rest and in IL-1 stimulated cells, respectively. Antiinflammatory drugs have different capacities to inhibit COX enzyme in human articular chondrocytes.

Exploring the conformational properties of the sequence space between two proteins with different folds: an experimental study

We have examined the conformational properties of 27 polypeptides whose sequences are hybrids of two natural protein domains with 8 % sequence identity and different structures. One of the natural sequences (spectrin SH3 domain) was progressively mutated to get closer to the other sequence (protein G B1 domain), with the only constraint of maintaining the residues at the hydrophobic core. Only two of the mutants are folded, each of them having a large sequence identity with one of the two natural proteins. The rest of the mutants display a wide range of structural properties, but they lack a well-defined three-dimensional structure, a result that is not recognized by computational tools commonly used to evaluate the reliability of structural models. Interestingly, some of the mutants exhibit cooperative thermal denaturation curves and a signal in the near-ultraviolet circular dichroism spectra, both typical features of folded proteins. However, they do not have a well-dispersed nuclear magnetic resonance spectrum indicative of a defined tertiary structure. The results obtained here show that both the hydrophobic core residues and the surface residues are important in determining the structure of the proteins, and suggest that the appearance of a completely new fold from an existing one is unlikely to occur by evolution through a route of folded intermediate sequences.

Beta-hairpin and beta-sheet formation in designed linear peptides

Recent knowledge about the determinants of beta-sheet formation and stability has notably been improved by the structural analysis of model peptides with beta-hairpin structure in aqueous solution. Several experimental studies have shown that the turn region residues can not only determine the stability, but also the conformation of the beta-hairpin. Specific interstrand side-chain interactions, hydrophobic and polar, have been found to be important stabilizing interactions. The knowledge acquired in the recent years from peptide systems, together with the information gathered from mutants in proteins, and the analysis of known protein structures, has led to successful design of a folded three-stranded monomeric beta-sheet structure.

High populations of non-native structures in the denatured state are compatible with the formation of the native folded state

The structures of the denatured states of the spectrin SH3 domain and a mutant designed to have a non-native helical tendency at the N terminus have been analyzed under mild acidic denaturing conditions by nuclear magnetic resonance methods with improved resolution. The wild-type denatured state has little residual structure. However, the denatured state of the mutant has an approximately 50% populated helical structure from residues 2 to 14, a region that forms part of the beta-sheet structure in the folded state. Comparison with a peptide corresponding to the same sequence shows that the helix is stabilized in the whole domain, likely by non-local interactions with other parts of the protein as suggested by changes in a region far from the mutated sequence. These results demonstrate that high populations of non-native secondary structure elements in the denatured state are compatible with the formation of the native folded structure.

Survival analysis of 306 European Spanish patients with systemic lupus erythematosus

OBJECTIVE

To describe survival of lupus in South European Spanish patients.

PATIENTS AND METHODS

Observational study of all SLE Spanish patients seen at three University Hospitals between 1975 and 1993. The charts of all patients were retrospectively reviewed. Sixty-four clinic and laboratory variables were extracted from charts. Univariate analysis, multivariate Cox proportional hazard regression analysis, actuarial life tables and multiple logistic regression analysis were used to calculate survival probability and identify variables associated with survival.

RESULTS

Three hundred and six (275 female and 31 male) patients were identified. Their mean age at diagnosis was 31.9 years (range 4 to 85). The mean duration of followup was 79 (1-126) months. Thirty-one patients died. The most common cause of death was infection (29%). Five, 10 and 15 years' survival rate was 90%+/-0.0158, 85%+/-0.0262 and 80%+/-0.0413, respectively. Log-rank analysis showed that male sex, proteinuria and nephropathy at diagnosis were associated with poor survival. By univariate and multivariate analysis male gender, nephropathy and CNS involvement were associated with worse survival.

CONCLUSION

In SLE patients from Spain, rate of survival is similar to other Caucasian patients, and better than other ethnic groups of Spanish ancestry. Other factors rather than genetic factors could explain our findings.

Osteoarthritis chondrocytes die by apoptosis. A possible pathway for osteoarthritis pathology

OBJECTIVE

To determine which kind of cell death occurs in cartilage from patients with osteoarthritis (OA).

METHODS

Seven normal and 16 OA cartilage samples were collected at autopsy or during joint replacement surgery, respectively. A piece of cartilage was cryopreserved until histologic studies were done. The rest of the cartilage was used to isolate chondrocytes. Apoptotic chondrocytes were analyzed by light and fluorescence microscopy using nuclear 4',6-diamidino-2-phenylindole dihydrochloride stain. Apoptotic chondrocytes were quantified by fluorescence-activated cell sorter (FACS) analysis. The TUNEL technique was used to study histologic apoptosis in situ. Superficial cartilage was processed for ultrastructural study by electron microscopy.

RESULTS

OA chondrocytes displayed nuclear and cytoplasmic changes consistent with apoptotic cell death. FACS analysis showed that the OA cartilage had a higher proportion of apoptotic chondrocytes than did normal tissue (51% versus 11%; P < 0.01). In situ study of DNA fragmentation in the cartilage showed that apoptotic cells were located in the superficial and middle zones. Ultrastructural analysis of the superficial OA cartilage revealed some empty lacunae, lysosomal-like structures, matrix vesicle-like structures, fragmented chondrocytes, and nuclear condensation.

CONCLUSION

Chondrocytes in OA cartilage demonstrated morphologic changes that are characteristic features of apoptosis. This mechanism of cell death plays an important role in the pathogenesis of OA and could be targeted for new treatment strategies.

Role of beta-turn residues in beta-hairpin formation and stability in designed peptides

The sequence RGITVNGKTYGR has been reported as part of a de novo design peptide system. This peptide folds as a beta-hairpin structure with three residues per strand and two residue turns. Asn6 side-chain, the residue in position L1 of the beta-turn, appeared to be solvent exposed, interacting only within the turn but not with the rest of the peptide. We have chosen this position as a good candidate to design mutations, based on the protein database statistical abundances, that should mainly affect the turn stability and possibly the pairing between strands. We have found that all NMR parameters, in particular the conformational shift analysis of CalphaH and the coupling constants, 3JHNalpha, correlate very well and show similar conformational features in all the turn mutant peptides. The population estimates are in reasonable agreement among the different methods used. It appears that the peptide with Asn in position L1 is the most structured peptide, followed by the one with Asp6. The next structured peptide is the one with Gly6. The least populated peptides were those with Ala6 and Ser6. We have found a strong correlation between the hairpin population, as determined from the conformational shift of CalphaH and the occurrence of the different residues at position L1 of beta-hairpins with type I' beta-turn, in the protein database. Our analysis demonstrates that this peptide system is sensitive enough to register small energy changes in the hairpin structure; therefore, it constitutes an appropriate model to quantify energy contributions, once the appropriate sheet/coil transition algorithm is developed. Comparison with the other studies indicate that the design of a specific hairpin structure must involve a sequence at the turn region favouring the desired turn type, and a sequence at the strands that avoids alternative interstrand side-chain pairings.

1H and 15N NMR assignment and solution structure of the SH3 domain of spectrin: comparison of unrefined and refined structure sets with the crystal structure

The assignment of the 1H and 15N nuclear magnetic resonance spectra of the Src-homology region 3 domain of chicken brain alpha-spectrin has been obtained. A set of solution structures has been determined from distance and dihedral angle restraints, which provide a reasonable representation of the protein structure in solution, as evaluated by a principal component analysis of the global pairwise root-mean-square deviation (rmsd) in a large set of structures consisting of the refined and unrefined solution structures and the crystal structure. The solution structure is well defined, with a lower degree of convergence between the structures in the loop regions than in the secondary structure elements. The average pairwise rmsd between the 15 refined solution structures is 0.71 +/- 0.13 A for the backbone atoms and 1.43 +/- 0.14 A for all heavy atoms. The solution structure is basically the same as the crystal structure. The average rmsd between the 15 refined solution structures and the crystal structure is 0.76 A for the backbone atoms and 1.45 +/- 0.09 A for all heavy atoms. There are, however, small differences probably caused by intermolecular contacts in the crystal structure.

Conformational analysis of peptides corresponding to all the secondary structure elements of protein L B1 domain: secondary structure propensities are not conserved in proteins with the same fold

The solution conformation of three peptides corresponding to the two beta-hairpins and the alpha-helix of the protein L B1 domain have been analyzed by circular dichroism (CD) and nuclear magnetic resonance spectroscopy (NMR). In aqueous solution, the three peptides show low populations of native and non-native locally folded structures, but no well-defined hairpin or helix structures are formed. In 30% aqueous trifluoroethanol (TFE), the peptide corresponding to the alpha-helix adopts a high populated helical conformation three residues longer than in the protein. The hairpin peptides aggregate in TFE, and no significant conformational change occurs in the NMR observable fraction of molecules. These results indicate that the helical peptide has a significant intrinsic tendency to adopt its native structure and that the hairpin sequences seem to be selected as non-helical. This suggests that these sequences favor the structure finally attained in the protein, but the contribution of the local interactions alone is not enough to drive the formation of a detectable population of native secondary structures. This pattern of secondary structure tendencies is different to those observed in two structurally related proteins: ubiquitin and the protein G B1 domain. The only common feature is a certain propensity of the helical segments to form the native structure. These results indicate that for a protein to fold, there is no need for large native-like secondary structure propensities, although a minimum tendency to avoid non-native structures and to favor native ones could be required.

Role of a nonnative interaction in the folding of the protein G B1 domain as inferred from the conformational analysis of the alpha-helix fragment

BACKGROUND

The role of local interactions in protein folding and stability can be investigated by the conformational analysis of protein fragments. The hydrophobic staple and Schellman motifs have been described at the N and C terminus, respectively, of protein alpha-helices. These motifs are characterized by an interaction between two hydrophobic residues, one outside the helix and one within the helix, and their importance for helix stability has been analyzed in model peptides. In the alpha-helix of the protein G B1 domain, only the Schellman motif is formed--the hydrophobic staple motif is absent despite the favourable sequence pattern. We have experimentally analyzed the solution conformation of the 19-41 fragment of protein G. This peptide comprises the helical residues and contains both the hydrophobic staple and Schellman motif sequences.

RESULTS

In the isolated peptide in water, the hydrophobic staple motif is formed and stabilizes the helical structure as compared with a shorter peptide lacking it, but the Schellman motif is not formed. In 30% aqueous TFE, the helix is more stable than in pure water and both motifs are formed.

CONCLUSIONS

The results suggest that the importance of each motif for the folding and stability of protein G is different. The nonnative hydrophobic staple interaction can help to nucleate the helix at the beginning of folding but has later to be disrupted. The Schellman motif, while not providing enough energy for substantial helix stabilization in the unfolded state, could be important for determining the local fold of the sequence in the context of the rest of the protein.

De novo design and structural analysis of a model beta-hairpin peptide system

We have designed de novo a simple, context-free, model linear peptide system to fold into a regular beta-hairpin structure, with three-residue beta-strands connected by a type I' beta-turn. CD and NMR analysis of this peptide in aqueous solution show that the peptide folds into the expected conformation. Structural characterization of three peptide variants in which some of the strand side-chains have been substituted by alanine, demonstrates that inter-strand side chain-side chain interactions are essential for beta-hairpin formation. This simple model system will help to isolate the factors behind beta-sheet formation, and contribute useful information about de novo protein design.

Infrared evidence of a beta-hairpin peptide structure in solution

The IR spectrum of an 16-amino acid peptide corresponding, according to NMR studies, to a beta-hairpin has been analysed. Two characteristic features distinguish its spectrum from that of an antiparallel beta-sheet: the low-frequency band that in a beta-sheet structure is located at approximately 1632 cm-1 appears here at approximately 1620 cm-1, and the high-frequency component does not undergo the isotopic shift typical of beta-sheet from 1690 to 1675 cm-1 when transferred to D2O. The infrared characteristics associated with beta-hairpins have been described so far in two proteins, in one of which, whose three-dimensional structure is known from X-ray diffraction, a beta-hairpin has actually been detected.

ILA, a member of the human nerve growth factor/tumor necrosis factor receptor family, regulates T-lymphocyte proliferation and survival

ILA, a gene induced by lymphocyte activation, is a member of the human nerve growth factor tumor necrosis factor receptor family and the human homologue of murine 4-1BB. The present study analyzed the role of ILA in the regulation of human peripheral blood T-lymphocyte function. Antibodies raised against different fusion proteins recognized ILA on activated lymphocytes. These antibodies significantly increased anti-CD3--induced T-lymphocyte proliferation. When anti-CD3--stimulated cells were incubated on ILA-expressing CHO cells, proliferation was inhibited. CHO cells transfected with a control construct and not expressing ILA did not reduce T-cell proliferation. A purified fusion protein containing the extracellular domain of ILA and the constant domain of human IgG (ILA-IgG) also inhibited lymphocyte proliferation. Results obtained by 3H-thymidine incorporation were confirmed by cell cycle analysis that showed a decrease in the number of lymphocytes in S phase. Lymphocyte morphology in cultures with ILA-expressing CHO cells was suggestive of apoptosis. Flow cytometry on propidium iodide-stained cells showed a time-dependent increase in the number of hypodiploid apoptotic cells when lymphocytes were cultured on ILA-expressing CHO cells. Internucleosomal DNA cleavage was seen in these cultures, but not in the presence of ILA-negative CHO cells. Studies on the mechanism by which ILA regulates T-cell function showed that ILA-IgG inhibited anti-CD3-induced T-cell proliferation when presented in immobilized but not in soluble form. These results suggest that ILA may act by cross-linking its ligand and thereby inhibit T-cell proliferation.

Idiopathic eosinophilic synovitis. Case report and review of the literature

Eosinophilia of synovial fluid is an uncommon condition. The majority of the reported cases are associated to diseases such as rheumatoid arthritis, parasitic disease, hypereosinophilic syndrome, Lyme disease, and allergic processes as well as hemarthrosis and arthrography. Presently there are only four cases of eosinophilic synovitis with unknown cause. We are reporting a patient with oligoarthritis of the knees, massive eosinophilia, and Charcot-Leyden crystals in synovial fluid without associated cause. We review the clinical and biological features of eosinophilic synovitis and discuss its pathogenesis.

Magnetic resonance imaging of the brain in systemic lupus erythematosus

Magnetic resonance imaging (MRI) of the brain is a sensitive method to detect parenchymal tissue lesions. Its value in the diagnosis of central nervous system (CNS) lupus is disputed. To address this question, we have conducted an open and prospective study in a population of 44 SLE patients. We investigated 24 patients (mean age 33 +/- 13 yr) with past or active CNS lupus (group A) that included organic brain syndrome (12), migraine (8), focal neurological signs (7), seizures (2), myelopathy (1) and narcolepsy-cataplexy (1), and 20 patients (mean age 32 +/- 12 yr) without CNS lupus (group B). Health controls comprising nine females and one male aged 31 +/- 9 yr were also studied for comparison (group C). MRI was performed using sagittal T1-weighted images, axial and coronal spin density, and T2-weighted images. All scans were read blindly. Thirteen patients in group A and 10 in group B had well-identified lesions on sequences with long repetition time. Lesions were mostly multiple, small, punctate areas of increased signal at periventricular or subcortical white matter of both cerebral hemispheres. The number and location of lesions were not significantly different in both groups. None of the group C patients had MRI lesions. The presence of lesions was significantly associated with age at study and disease duration, but not with the presence of CNS lupus. In summary, MRI abnormalities are detected in neurologically asymptomatic SLE patients. Whether this represents subclinical brain involvement remains unknown.

Survival analysis of disease modifying antirheumatic drugs in Spanish rheumatoid arthritis patients

OBJECTIVES

To evaluate the duration of treatment and the reasons for discontinuing therapy with disease modifying antirheumatic drugs in Spanish rheumatoid arthritis patients.

METHODS

An observational study was made of 629 patients with rheumatoid arthritis treated with disease modifying antirheumatic drugs between 1979 and 1991. The outcomes (treatment termination because of toxicity and lack of response) of 991 treatment starts with intramuscular gold salts, D-penicillamine, azathioprine, and methotrexate were subjected to survival analysis. Cumulative probability of continuation of each drug (drug survival) was calculated by the Kaplan-Meier method and comparison between the survival curve of each was made by log rank testing.

RESULTS

Median drug survival (95% confidence interval) was 51 (25-76.9) months for methotrexate, 39.9 (19.9-48.2) months for azathioprine, 34.9 (29.4-41.4) months for gold salts, and 16.4 (13.9-21) months for D-penicillamine. The highest cumulative probability of drug survival at five years was for methotrexate (45%); that at 10 years was for gold salts (15%). Up to 60% of the patients discontinued D-penicillamine in the first two years. Lack of response was the major limiting factor for all drugs except D-penicillamine, for which it was toxicity. D-Penicillamine was associated with a greater rate of discontinuations because of toxicity in women and patients older than 65. Previous disease modifying antirheumatic drug administration did not influence current drug survival.

CONCLUSION

Overall, gold salts remain useful for the treatment of rheumatoid arthritis over long periods of time in the population studied. Because of the high rate of continuation of treatment (survival) and the optimal efficacy and toxicity profiles observed with methotrexate after five years of treatment, it should be the drug of first choice for second line treatment of these RA patients.

Interactions responsible for the pH dependence of the beta-hairpin conformational population formed by a designed linear peptide

In a previous work [Blanco, F.J., Jiménez, M.A., Herranz, J., Rico, M., Santoro, J. & Nieto, J. L. (1993) J. Am. Chem. Soc. 115, 5887-5888] we showed that a short, designed linear peptide, YQNPDGSQA (peptide 1), can form a monomeric beta hairpin in aqueous solution. The pH dependence of the beta-hairpin conformation formed by the designed peptide and a series of related peptides has been examined in this work using 1H-NMR methods. Three pH-dependent interactions have been identified: a local interaction, unimportant structurally, between the C-terminal carboxylate group and the side-chain amide group of Q8; an electrostatic interaction between the main-chain N-terminus and C-terminus; and a hydrogen bond involving the side-chain amide protons of N3 and the side-chain carboxylate group of D5. The latter two interactions are particularly relevant as they increase the population of the beta-hairpin conformation. We also observe in the mutant peptide A9H that the interaction between Y1 and H9 (of the type proposed to exist in proteins) does not contribute to beta-hairpin stabilisation in our peptide system. Peptide 1 is, therefore, a very suitable model to examine the different interactions that contribute to beta-hairpin stability.

The distribution of alpha-helix propensity along the polypeptide chain is not conserved in proteins from the same family

We address the question of whether the distribution of secondary structure propensities of the residues along the polypeptide chain (denominated here as secondary structure profiles) is conserved in proteins throughout evolution, for the particular case of alpha-helices. We have analyzed by CD the conformation of peptides corresponding to the five alpha-helices of two alpha/beta parallel proteins (ComA and Ara). The large alpha-helical population of peptide ComA-4 detected by CD in aqueous solution has been confirmed by NMR. These proteins are members of the CheY and P21-ras families, respectively, which have been studied previously in the same way (Muñoz V, Jiménez MA, Rico M, Serrano L, 1995, J Mol Biol 245:275-296). Comparison of the helical content of equivalent peptides reveals that protein alpha-helix propensity profiles are not conserved. Some equivalent peptides show very different helical populations in solution and this is especially evident in very divergent proteins (ComA and CheY). However, all the peptides analyzed so far adopted an important population of helical conformations in the presence of 30% trifluoroethanol, indicating that there could be a conserved minimal requirement for helical propensity.

[Clinical and serological manifestations of 307 Spanish patients with systemic lupus erythematosus. Comparison with other ethnic groups]

There is evidence suggesting that clinical manifestations and severity in systemic lupus erythematosus (SLE) are associated with age, sex and ethnicity. The influence of genetic factors, particularly HLA antigens, on disease expression is revealed by the diversity of clinical conditions in patients from different ethnic groups. The aim of this work was to analyze the impact of demographic factors on SLE expression in the Spanish population. Therefore, a retrospective analysis was undertaken of clinical records of 307 patients diagnosed in three Rheumatology Services, with a mean follow-up of 79 months. The distribution of clinical manifestations according to age and sex was studied and compared with those observed in other ethnic groups. The results show the influence of sex and age on our patient population. Thus, female had a higher frequency of malar rash, photosensitivity and lymphopenia. Males had a higher CNS and renal involvement. Patients under 15 years had a higher involvement of CNS and kidney. Patients under 15 years had a higher frequency of nephropathy, hematological, cutaneous and CNS changes. Patients older than 50 had a higher frequency of pleuropericarditis, but without renal involvement. Our ethnic group expressed a disease with a severity similar to that observed in north-european caucasians, higher than in north-american caucasians and lower than in south-american caucasians, asiatic and africans. In conclusion, patients with SLE from the south-european ethnic groups express a clinical picture with characteristics and severity similar to those observed in europeans from other latitudes and different from those reported in other ethnic groups.

Regulation of cyclooxygenase-2 expression in normal human articular chondrocytes

This study analyzes cyclooxygenase II (COX-2) gene expression, protein synthesis, and PGE2 release in normal human articular chondrocytes. Stimulation of chondrocytes in primary culture resulted in a dose-dependent induction of COX-2 mRNA in response to IL-1 with an ED50 between 0.1 and 1 ng/ml. COX-2 mRNA was detectable after 2 h, reached high levels at 6 h, and showed a remarkably long duration of expression for at least 72 h. Analysis of other extracellular stimuli showed that COX-2 mRNA was inducible by other cytokines including TNF-alpha, IL-6, and LIF and by bacterial LPS. Dexamethasone completely inhibited IL-1-induced COX-2 mRNA expression. Analysis of signaling pathways showed that PMA and calcium ionophore A23187, but not dibutyryl cAMP, induced COX-2 mRNA. The combination of IL-1 and A23187 resulted in synergistic increases. IL-1 effects were not reduced by the protein kinase C inhibitor staurosporine or by the protein kinase A inhibitor H89 but blocked by the protein tyrosine kinase inhibitor herbimycin A. COX-2 protein was detected at 71 kDa by Western blotting in IL-1-stimulated, and to almost similar levels in A23187-treated, cells. Flow cytometric analysis showed that after IL-1 stimulation 78% of the chondrocytes expressed COX-2 protein. The patterns of COX-2 protein expression and the levels of PGE2 release correlated with the effects of the different stimuli and inhibitors on mRNA expression.

Regulation of cyclooxygenase-2 expression in normal human articular chondrocytes

This study analyzes cyclooxygenase II (COX-2) gene expression, protein synthesis, and PGE2 release in normal human articular chondrocytes. Stimulation of chondrocytes in primary culture resulted in a dose-dependent induction of COX-2 mRNA in response to IL-1 with an ED50 between 0.1 and 1 ng/ml. COX-2 mRNA was detectable after 2 h, reached high levels at 6 h, and showed a remarkably long duration of expression for at least 72 h. Analysis of other extracellular stimuli showed that COX-2 mRNA was inducible by other cytokines including TNF-alpha, IL-6, and LIF and by bacterial LPS. Dexamethasone completely inhibited IL-1-induced COX-2 mRNA expression. Analysis of signaling pathways showed that PMA and calcium ionophore A23187, but not dibutyryl cAMP, induced COX-2 mRNA. The combination of IL-1 and A23187 resulted in synergistic increases. IL-1 effects were not reduced by the protein kinase C inhibitor staurosporine or by the protein kinase A inhibitor H89 but blocked by the protein tyrosine kinase inhibitor herbimycin A. COX-2 protein was detected at 71 kDa by Western blotting in IL-1-stimulated, and to almost similar levels in A23187-treated, cells. Flow cytometric analysis showed that after IL-1 stimulation 78% of the chondrocytes expressed COX-2 protein. The patterns of COX-2 protein expression and the levels of PGE2 release correlated with the effects of the different stimuli and inhibitors on mRNA expression.

Folding of protein G B1 domain studied by the conformational characterization of fragments comprising its secondary structure elements

The solution structure of the isolated fragments 1-20 (beta-hairpin), 21-40 (alpha-helix) and 41-56 (beta-hairpin), corresponding to all the secondary structure elements of the protein G B1 domain, have been studied by circular dichroism and nuclear magnetic resonance techniques. In the protein G B1-(1-20) fragment turn-like folded structures were detected in water though low populated. In the presence of 30% aqueous trifluoroethanol there is a complex conformational behaviour in which a helical structure at the N-terminal half is formed in equilibrium with random and native-like beta-hairpin structures. The peptide corresponding to the alpha-helix is predominantly unstructured in water, while in 30% trifluoroethanol it highly populates a native alpha-helical conformation, including a (i,i + 5) interaction between hydrophobic residues at its C-terminus. The third peptide was previously reported to form a monomeric native beta-hairpin structure in water [Blanco, F. J., Rivas, G. & Serrano, L. (1994a) Nature Struc. Biol. 1, 584-590]. We show in this work that the beta-hairpin structure is further stabilized in 30% trifluoroethanol and destabilised in the presence of 6 M urea, though some folded structure persists even in these highly denaturing conditions. The conformational properties of these peptides suggests that the second beta-hairpin could be an important folding initiation site on which the rest of the chain folds. Reconstitution experiments failed to show evidence of interaction between the peptides. Algorithms designed to predict the helical and extended conformations of peptides in aqueous solution successfully describe the complicated behaviour of these peptides. Comparison of the predicted and the experimental results with those for a structurally related protein, ubiquitin, shows very strong similarities, the main difference being the switch of the most stable beta-hairpin from the N-terminus in ubiquitin to the C-terminus in protein G.

IL-1-induced nitric oxide inhibits chondrocyte proliferation via PGE2

IL-1 inhibits chondrocyte proliferation induced by TGF beta or serum. This study analyzed the role of nitric oxide (NO), which is induced at high levels by IL-1 in chondrocytes. NO, when administered through sodium nitroprusside (SNP), inhibited TGF beta or serum-induced chondrocyte proliferation. To determine whether IL-1-induced NO is responsible for growth inhibition by IL-1, chondrocytes were cultured in the presence of the nitric oxide synthase inhibitor N-monomethyl-L-arginine (NMA), which dose-dependently reduced the antiproliferative effects of IL-1. Analysis of interactions between PGE2, a known chondrocyte growth inhibitor, and NO showed that PGE2 does not induce NO and is not required for NO induction by IL-1. However, SNP induced high levels of PGE2, and NMA reduced IL-1-induced PGE2. This raised the possibility that PGE2 is a downstream mediator of the antiproliferative effects of NO. This was confirmed in experiments where the growth inhibitory effects of SNP were reduced by indomethacin. These results suggest that the chondrocyte growth inhibition by IL-1 in chondrocytes is due to the induction of NO, which stimulates the production of PGE2 as a mediator of its antiproliferative effects.

The hydrophobic-staple motif and a role for loop-residues in alpha-helix stability and protein folding

A recurrent local structural motif is described at the amino terminus of alpha-helices, that consists of a specific hydrophobic interaction between a residue located before the N-cap, with a residue within the helix (i,i+5 interaction). NMR and CD analysis of designed peptides demonstrate its presence in aqueous solution, its contribution to alpha-helix stability and its role in defining the alpha-helix N terminus limit. Comparison between the N-terminal structures of the peptide and those in proteins with the same fingerprint sequence, shows striking similarities. The change in the polypeptide chain direction produced by the motif suggests an important role in protein folding for residues located in polypeptide segments between secondary structure elements.

Differentiation-dependent effects of IL-1 and TGF-beta on human articular chondrocyte proliferation are related to inducible nitric oxide synthase expression

This study analyzed the effect of chondrocyte differentiation on iNOS expression and responses to IL-1 and TGF-beta. During subculturing of chondrocytes, the growth-stimulatory effects of TGF-beta decreased, and cells in later passages even were growth inhibited by TGF-beta. IL-1 beta responses showed an inverse pattern. The antiproliferative effects of IL-1 beta decreased, and, after passage 6, IL-1 beta became a growth stimulator for chondrocytes. This change in growth factor response pattern was associated with a decrease in type II collagen expression. To determine whether these changes in the growth regulatory effects of IL-1 beta and TGF-beta were related to nitric oxide (NO), inducible nitric oxide synthase (iNOS) expression and NO release were analyzed. In primary chondrocytes, TGF-beta did not stimulate iNOS mRNA expression or NO release, and, during co-incubation, it did not detectably alter the IL-1 beta effect. Preincubation with TGF-beta resulted in a time-dependent increase in IL-1-induced NO. With increasing passage number, the IL-1 beta effects decreased, and, after passage 6, IL-1 beta no longer detectably stimulated iNOS expression or NO release. However, TGF-beta increased NO production synergistically with IL-1 beta during the same culture period when it lost its growth-stimulatory effects. The antiproliferative effects of TGF-beta in late passage chondrocytes were reversed by the NO synthase inhibitor NG-monomethylarginine. These results suggest a novel pattern of iNOS regulation by IL-1 and TGF-beta and show that the factors that modulate iNOS expression and proliferation are dependent on the differentiation status of the cells.

Differentiation-dependent effects of IL-1 and TGF-beta on human articular chondrocyte proliferation are related to inducible nitric oxide synthase expression

This study analyzed the effect of chondrocyte differentiation on iNOS expression and responses to IL-1 and TGF-beta. During subculturing of chondrocytes, the growth-stimulatory effects of TGF-beta decreased, and cells in later passages even were growth inhibited by TGF-beta. IL-1 beta responses showed an inverse pattern. The antiproliferative effects of IL-1 beta decreased, and, after passage 6, IL-1 beta became a growth stimulator for chondrocytes. This change in growth factor response pattern was associated with a decrease in type II collagen expression. To determine whether these changes in the growth regulatory effects of IL-1 beta and TGF-beta were related to nitric oxide (NO), inducible nitric oxide synthase (iNOS) expression and NO release were analyzed. In primary chondrocytes, TGF-beta did not stimulate iNOS mRNA expression or NO release, and, during co-incubation, it did not detectably alter the IL-1 beta effect. Preincubation with TGF-beta resulted in a time-dependent increase in IL-1-induced NO. With increasing passage number, the IL-1 beta effects decreased, and, after passage 6, IL-1 beta no longer detectably stimulated iNOS expression or NO release. However, TGF-beta increased NO production synergistically with IL-1 beta during the same culture period when it lost its growth-stimulatory effects. The antiproliferative effects of TGF-beta in late passage chondrocytes were reversed by the NO synthase inhibitor NG-monomethylarginine. These results suggest a novel pattern of iNOS regulation by IL-1 and TGF-beta and show that the factors that modulate iNOS expression and proliferation are dependent on the differentiation status of the cells.

The order of secondary structure elements does not determine the structure of a protein but does affect its folding kinetics

We have analyzed the structure, stability and folding kinetics of circularly permuted forms of alpha-spectrin SH3 domain. All the possible permutations involving the disruption of the covalent linkage between two beta-strands forming a beta-hairpin have been done. The different proteins constructed here fold to a native conformation similar to that of wild-type protein, as demonstrated by nuclear magnetic resonance and circular dichroism. Although all the mutants have similar stabilities (they are 1 to 2 kcal mol-1 less stable than the wild-type) their rate constants for folding and unfolding are quite different. Protein engineering, in combination with kinetics indicates that the folding pathway has been changed in the circularly permuted proteins. We conclude that neither the order of secondary structure elements, nor the preservation of any of the beta-hairpins present in this domain, is crucial for the ability of the polypeptide to fold, but they influence the folding and unfolding kinetics and could determine its folding pathway.

Cytokine regulation of chondrocyte functions

Regulation of chondrocyte secretory functions and proliferation by cytokines and growth factors is central to cartilage development and maintenance of homeostasis in the mature organism. Depending on the type of extracellular stimulus, chondrocytes can be induced to enter a catabolic matrix degrading or anabolic matrix forming functional program. Interleukin I and transforming growth factor beta are the prototypic stimuli for the catabolic and anabolic program, respectively. Insight into the regulation of chondrocytes by cytokines and growth factors provides the basis for improved concepts of osteoarthritis pathogenesis and new perspectives for therapeutic interventions.

Chondrocyte apoptosis induced by nitric oxide

Chondrocytes stimulated with IL-1 produce high levels of nitric oxide (NO), which inhibits proliferation induced by transforming growth factor-beta or serum. This study analyzes the role of NO and IL-1 in the induction of chondrocyte cell death. NO generated from sodium nitroprusside induced apoptosis in cultured chondrocytes as demonstrated by electron microscopy, 4',6-dianidino-2-phenylindole dihydrochloride staining, FACS analysis, and histochemical detection of DNA fragmentation. Similar results were obtained with two other NO donors, 3-morpholinosynonimide-hydrochloride and s-nitroso-N-acetyl-D-L-penicillamine. In contrast, oxygen radicals generated by hypoxanthine/xanthine oxidase caused necrosis but did not induce chondrocyte apoptosis. To analyze whether endogenously generated NO induces apoptosis, chondrocytes were stimulated with IL-1, but there was no evidence for apoptotic changes. Combinations of NO inducers such as IL-1, lipopolysaccharide, tumor necrosis factor, and interferon-gamma also failed to trigger apoptosis. IL-1-stimulated chondrocytes are known to produce oxygen radicals that react with NO to form products that can induce cell death in other systems. We thus tested IL-1 in combination with the oxygen radical scavengers N-acetyl cysteine, dimethyl sulfoxide, or 5,5'-dimetylpyrroline 1-oxide. Under these conditions IL-1 was able to induce apoptosis, which was inhibited in a dose-dependent manner by the NO synthase inhibitor N-monomethyl L-arginine. Conversely, endogenous oxygen radicals induced by inflammatory mediators caused necrosis under conditions in which the simultaneous production of NO was reduced. These results suggest that NO, but not oxygen radicals, is the primary inducer of apoptosis in human articular chondrocytes.

Anadamide, an endogenous cannabinoid receptor agonist inhibits lymphocyte proliferation and induces apoptosis

This study examined the immunoregulatory effects of anadamide, the recently identified first endogenous cannabinoid receptor ligand. Anadamide caused dose-dependent inhibition of mitogen-induced T and B lymphocyte proliferation. Its potency was 3- and 10-fold less than that of the synthetic cannabinoids delta 8-tetrahydrocannabinol (delta 8-THC) and CP55940, respectively. Anadamide effects on DNA synthesis in T and B lymphocytes occurred rapidly as exposure of the cells during the final 4 h of culture was sufficient to achieve > 40% inhibition. Low doses of anadamide which caused significant inhibition of lymphocyte proliferation caused DNA fragmentation as demonstrated by immunohistochemistry, FACS analysis and Southern blotting. Apoptosis was also induced by high concentrations of delta 8-THC, but not by CP55940. Brain and peripheral cannabinoid receptor mRNA was expressed in PBMC with varying levels between individual donors. In summary, these findings demonstrate immunosuppressive effects of anadamide which are associated with inhibition of lymphocyte proliferation and the induction of cell death by apoptosis.

A short linear peptide that folds into a native stable beta-hairpin in aqueous solution

The conformational properties of a 16 residue peptide, corresponding to the second beta-hairpin of the B1 domain of protein G, have been studied by nuclear magnetic resonance spectroscopy (NMR). This fragment is monomeric under our experimental conditions and in pure water adopts a population containing up to 40% native-like beta-hairpin structure. The detection by NMR of a native-like beta-hairpin in aqueous solution, reported here for the first time, indicates that these structural elements may have an important role in the early steps of protein folding. It also provides a good model to study in detail the sequence determinants of beta-hairpin structure stability, as has been done with alpha-helices.

NMR solution structure of the isolated N-terminal fragment of protein-G B1 domain. Evidence of trifluoroethanol induced native-like beta-hairpin formation

The solution structure of the isolated N-terminal fragment of streptococcal protein-G B1 domain has been investigated in H2O and TFE/H2O solution by CD and NMR to gain insight into the possible role that native beta-hairpin secondary structure elements may have in early protein folding steps. The fragment also has been studied under denaturing conditions (6 M urea), and the resulting NMR chemical shifts were used as a reference for the disordered state. On the basis of CD and NMR data, it is concluded that in aqueous solution the fragment is basically flexible, with two local low populated chain bends involving residues 8-9 and 14-15, respectively, in close agreement with secondary structure predictions, a structure that is different from the final folded state of that segment of the protein. The changes in the CD spectrum, the presence of several medium-range NOEs plus two long-range NOEs, and the sign of the H alpha conformational shifts reveal that the addition of TFE facilitates the formation of a set of transient beta-hairpins involving essentially the same residues that form the native beta-hairpin found in the final three-dimensional structure of the B1 domain. The stabilization of native-like structures by TFE is known to occur for helices, but, to our knowledge, this is the first time the stabilization of a native-like beta-hairpin structure by TFE is reported. Since long-range tertiary interactions are absent in the isolated fragment, our results support the idea that, in addition to helices, beta-hairpins may play an active role in directing the protein folding process.

Helix formation by the phospholipase A2 38-59 fragment: influence of chain shortening and dimerization monitored by nmr chemical shifts

The solution structure of a peptide fragment corresponding to the 38-59 region of porcine phospholipase A2 has been investigated using CD, nmr chemical shifts, and nuclear overhauser effects (NOEs). This isolated fragment of phospholipase forms an alpha-helix spanning residues 38-55, very similar to the one found in the native protein, except for residues 56-58, which were helical in the crystal but found random in solution. Addition of triflouroethanol (TFE) merely increased helix population but it did not redefine helix limits. To investigate how the folding information, in particular that concerning eventual helix start and stop signals, was coded in this particular amino acid sequence, the helices formed by synthetic peptides reproducing sections of this phospholipase 38-59 fragment, namely 40-59, 42-59, 38-50, and 45-57, were characterized using NOEs and helix populations quantitatively evaluated on different peptide chain segments using nmr chemical shifts in two solvents (H2O and 30% TFE/H2O). A set of nmr spectra was also recorded and assigned under denaturing conditions (6M urea) to obtain reliable values for the chemical shifts of each peptide in the random state. Based on chemical shift data, it was concluded that the helix formed by the phospholipase 38-59 fragment was not abruptly, but progressively, destabilized all along its length by successive elimination of residues at the N end, while the removal of residues at the C end affected helix stability more locally and to a lesser extent. These results are consistent with the idea that there are not single residues responsible for helix initiation or helix stability, and they also evidence an asymmetry for contributions to helix stability by residues located at the two chain ends. The restriction of molecular mobility caused by linking with a disulphide bridge at Cys 51 two identical 38-59 peptide chains did not increase helix stability. The helix formed by the covalently formed homodimer was very similar in length and population to that formed by the monomer.

Light, immunofluorescence and electron microscopy renal biopsy findings as predictors of mortality in eighty-five Spanish patients with systemic lupus erythematosus

This study aimed to define prognostic indicators of death in renal biopsies from Spanish patients with SLE. Renal biopsies of eighty-five lupus patients with and without clinical nephritis, taken between 1974 and 1987, were reviewed. Samples previously processed for light (LM), immunofluorescence (IM) and electron (EM) microscopy were analysed blind. Kaplan-Maier curves, log-rank test, and multivariate Cox's regression statistical methods were used for comparison of biopsy data in relation to patient survival. Univariate analysis showed that vascular hyalinosis, glomerular sclerosis, fibrous crescent and chronicity index higher than 3 by LM, and intramembranous dense-deposits by EM are predictors of poor survival. A multivariate approach confirmed the independent influence of vascular hyalinosis, chronicity index higher than 3 and intramembranous deposits. A predictive model can be constructed with three LM (hyalinosis, tubular atrophy and glomerular sclerosis) and three EM variables (subepithelial, mesangial and intramembranous deposits). Selected renal biopsy changes detected by LM and EM are therefore predictors of death in patients with lupus. Chronicity markers, more than those of activity or severity, are the best prognostic indicators.

Conformational behavior of Escherichia coli OmpA signal peptides in membrane mimetic environments

Nuclear magnetic resonance and circular dichroism (CD) studies of isolated peptides corresponding to WT and mutant OmpA signal sequences are reported; all of the peptides adopt substantial amounts of alpha-helical structure both in 1:1 (v/v) trifluoroethanol (TFE)/water and in sodium dodecyl sulfate (SDS) micelles. In TFE/water, the helix begins after the positively charged N-terminal residues and is most stable in the hydrophobic core, which correlates with results obtained previously for other signal sequences. The helix is weaker between the hydrophobic core and the C-terminus; such a break in the helix appears to be common to other signal peptides studied previously and could be of functional importance. No clear correlation could be established between the helicity of the peptides in TFE/water and their in vivo activities. All the peptides have a higher alpha-helix content in SDS than in TFE/water, and there is a good correlation between helix content in SDS and in vivo activity. Helicity in SDS for the functional peptides increases both at the N-terminus and in the hydrophobic core, and is driven by a strong association of the core with the hydrophobic chains of the detergent. The extension of the helix toward the N-terminus may be a result of neutralization of the N-terminal positive charges by the headgroups of the micelles, which removes unfavorable electrostatic interactions with the helix dipole. All these comparisons were facilitated by the use of upfield shifts of H alpha protons in helical regions relative to random coil chemical shifts, which also yielded estimates of helical content that correlated well with the CD results.

CD and 1H-NMR studies on the conformational properties of peptide fragments from the C-terminal domain of thermolysin

The propensity of the peptide fragments 233-248, 245-260, 258-276, 279-298 and 299-316 from the thermolysin C-terminal domain to form non-random structures has been examined by CD and two-dimensional NMR spectroscopy. The conformational properties of these fragments have been studied in aqueous solution and in the mixed solvent trifluoroethanol/H2O (3:7 by vol.). Small but detectable populations of helical structures (up to 10-20%) in aqueous solution have been found for the fragments 233-248, 279-298 and 299-316. These populations are remarkably enhanced (50-70%) in the more hydrophobic mixed solvent, where the fragment 258-276 also forms a comparable helical population. These four fragments are helical in the native crystal structure and the spanning of the corresponding helices in the isolated peptides in solution matches very closely the ones in the native structure. In contrast, the fragment 245-260, an omega-loop in the crystal, remains unstructured in both solvents. Medium-range NOE between protons in sidechains indicate the adoption of preferred sidechain conformations accompanying helix formation. Results are in agreement with the framework model of folding, in which native elements of secondary structure are formed first and folding follows from the collapse of these structural elements.

Characterization of a synthetic calmodulin-binding peptide derived from Bacillus anthracis adenylate cyclase

A 34-amino acid peptide corresponding to residues 532-565 of Bacillus anthracis adenylate cyclase (P532-565), a calmodulin (CaM)-activated enzyme, was synthesized by solid phase method. Although not homologous to any known CaM binding sequence, P532-565 exhibits molecular features characteristic of this class of peptides: a higher proportion of basic and hydrophobic residues, segregated onto the two faces of the alpha-helical structure. Fluorescence measurements and gel retardation analysis showed that P532-565 binds CaM in a Ca(2+)-dependent manner, with a binding energy that represents 80% of the binding energy of the adenylate cyclase-CaM complex. Circular dichroism analysis showed that P532-565 exists in solution as a mixture of random-coil and alpha-helical structures and that trifluoroethanol increases the relative proportion of alpha-helical population. Analysis of proton NMR spectrum in H2O allowed identification of the different amino acid spin systems and complete spectral assignment. The pattern of nuclear Overhauser effect connectivities, intense NN(i,i + 1) and medium range alpha N(i,i + 3) and alpha beta (i,i + 3) indicate the presence of an alpha-helix in the carboxylterminal end (between residues 551 and 563) in fast exchange with extended structures. These data, together with CaM-binding properties of Bordetella pertussis adenylate cyclase, show that despite rather divergent primary structures, the two bacterial enzymes possess similar structural organization of their binding sites for activator protein.

Periodic properties of proton conformational shifts in isolated protein helices. An experimental study

In this work, the helix-forming residues in fragments of several proteins (ribonuclease, thermolysin, tendamistat and angiogenin) were identified by NOE and the helix proton shifts were measured as delta changes associated with helix-population increments driven by trifluoroethanol addition. When estimated in this way, a regular pattern of helix conformational shifts was clearly seen in the delta delta versus sequence profiles of all the peptides studied. The helix periodicity of the H alpha and H beta resonances was especially clear, an observation that earlier statistical studies of protein delta values failed to predict. Amide protons showed the largest helix shifts, but with a less-sharply defined periodic character. Aromatic residues considerably distorted the periodicity of the helix amide shifts in some peptides, as evidenced by the delta shifts of a RNase A fragment 1-15 analog in which the two aromatic residues were replaced by Ala. The relationship between helix periodicity and peptide amphiphatic character is discussed.

The homologous angiogenin and ribonuclease N-terminal fragments fold into very similar helices when isolated

The solution structure of the N-terminal hexadecapeptide of human angiogenin, a protein of unknown tertiary structure, has been precisely delineated by the combined use of CD, NOE and secondary shift data. A helix that starts just after Ser 3 and ends at Asp 14 was stabilized in 30% trifluoroethanol. This helix is strikingly similar in origin and length to the one formed by its homologous, the S-peptide of Ribonuclease (conformationally reexamined here), despite their quite different sequences (only four conserved residues). These results support the idea that individual start and stop signals indeed govern the location and size of natural isolated helices.

Tendamistat (12-26) fragment. NMR characterization of isolated beta-turn folding intermediates

In order to determine whether regions of a protein that are turns in the native structure are able to maintain such a structure when isolated, we have studied the conformational properties of various peptide fragments corresponding to the 12-26-peptide region of the alpha-amylase inhibitor tendamistat, by NMR. Amide solvent accessibility, NOE spectroscopy (NOESY) and rotating-frame NOE spectroscopy (ROESY) data strongly support the conclusion that the 12-26 and 15-23 peptides adopt in aqueous solution, a set of turn-like structures located around the central region of their corresponding polypeptidic chains, the same region where a beta turn exists in the native protein. Such a set of structures are destabilized when one residue located within the native beta turn of the 15-23 peptide is modified Trp18----Ser. Our results indicate that the tendency to bend in a predetermined region of a protein chain seems to exist from the very beginning of the folding process and therefore it could drive the folding instead of being a consequence of the tertiary assembly of the protein.